► Small towns across the US face similar problems; tight budgets and pressing needs keep rising faster than revenues, resulting in many communities struggling to maintain…
(more)

▼ Small towns across the US face similar problems; tight budgets and pressing needs keep rising faster than revenues, resulting in many communities struggling to maintain a viable economic base. In response to this dilemma, local leaders in Georgia have been investing in public space development (often with the assistance of Public Service units at the University of Georgia) as a means of encouraging economic activity. However, one missing component in the outreach process is an overarching framework that guides resources towards those projects that can generate the greatest economic benefit to the community. This thesis explores the typologies of communities and their associated public space projects that are being implemented in an attempt to stimulate economic development. These project types are then evaluated to determine which endeavors tend to be most successful as catalysts for economic development, as a mechanism for determining where communities should focus their efforts.
Advisors/Committee Members: Katherine Melcher.

The use of heterogeneous catalysts containing Au nanoparticles supported on TiO2 has been explored for oxidative aqueous phase transformations of sustainable phenolic and benzoic acid…
(more)

▼

The use of heterogeneous catalysts containing Au
nanoparticles supported on TiO2 has been explored for oxidative
aqueous phase transformations of sustainable phenolic and benzoic
acid derivatives that can be obtained from lignin. Au/TiO2
catalysts were chosen because of their high activity for ambient
pressure oxidations of gas phase species, and because their
synthesis is facile and reproducible through a modified
deposition-precipitation method. The aerobic oxidation of syringic,
vanillic, and ferulic acid as well as of guaiacol, eugenol and
anisole was investigated at temperatures up to 70°C under (i)
atmospheric air sparging in an open reactor and (ii) at 10 atm air
pressure in a closed reactor system. The catalysts were
characterised by Transmission Electron Microscopy (TEM),
Inductively Coupled Plasma (ICP) Optical Emission Spectroscopy and
the reproducibility of their catalytic activity independently
monitored by determining their activity for carbon monoxide
oxidation in a gas flow reactor.The oxidation of syringic acid,
vanillic acid, ferulic acid over Au/TiO2 resulted in the formation
of 2,6-dimethoxy benzoquinone, guaiacol, and vanillin,
respectively, indicating high selectivity for decarboxylation
followed by selective oxidation at the position releasing the
leaving group. Guaiacol was found to form tetraguaiacol, while
eugenol produced quinone methide. Generally, higher air pressure
strongly accelerated the transformations, indicating that
availability of oxidants formed from O2 is the rate limiting step
in the observed transformations. No transformations took place when
O2 was excluded from the systems. Overall, guaiacol was found to
react fastest, followed by syringic acid, ferulic acid, then
vanillic acid. Anisole was found to be unreactive, even at elevated
air pressure. The overall reaction pattern emerging from these
studies is that the aerobic oxidation in the presence of Au/TiO2
mimics known biotransformations, for example peroxidase-catalysed
oxidations involving H2O2.To assess how the functional groups on
the aromatic ring influence reactivity the oxidation of
p-hydroxybenzoic acid and of 2,6-dimethoxybenzoic acid was also
assessed. It was found that decarboxylation of p-hydroxybenzoic
acid proceeds, albeit rather slowly, forming phenol, with no
further oxidation to hydroquinone or benzoquinone. Taken together
these results indicate that the methoxy moieties influence
reactivity through both their inductive and resonance effects:
leaving of the carboxylic acid group appears to be enhanced through
the inductive effect, while further oxidation at the phenolic site
seems to be activated through the resonance effect in
ortho-position. In line with this hypothesis, it was recently found
that dimethoxybenzoic acid converts fast.

► Single-site catalysts revolutionized the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently…
(more)

▼ Single-site catalysts revolutionized the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated-commodity resins. The key to their rapid success and industrial implementation resides in the fact that they can be used without major modifications in the polymerization reactors that previously used heterogeneous Ziegler-Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas-phase reactors, soluble single-site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities.
Metallocene catalysts have been supported on a variety of carriers, but supporting late transition metal catalysts has not been investigated in detail, despite their very interesting properties such as tolerance to polar comonomers and impurities, activity in the absence of MAO, and the formation of short chain branches by the chain walking mechanism. The research work of this PhD thesis intends to fill this gap, by developing supported late transition metal catalysts with high catalyst activities towards ethylene polymerization and good polymer particle morphology.
The effects of catalyst structure and polymerization conditions on silica-supported nickel diimine catalysts are discussed in Chapter 3. Compared with the equivalent homogeneous catalysts, the covalently-attached supported catalysts had high activities, produced spherical polyethylene particles with good morphologies, and polyethylene with higher melting temperatures, higher molecular weight averages, and broader molecular weight distributions. Borates used as internal activators during the synthesis of these supported catalysts successfully activated the nickel diimine complexes.
In Chapter 4, MgCl2/alcohol adducts are recrystallized with alkylaluminum compounds and used as catalysts supports for nickel diimine complexes functionalized with amine groups. Polymerization results were compared with those of the equivalent SiO2-supported nickel diimine catalysts. MgCl2-based supported nickel diimine catalysts had high catalyst activity without the use of activators, and it was possible to control polymer molecular weight averages by changing the support composition.
Although linear low density polyethylene made with metallocenes offers superior mechanical properties such as excellent toughness, impact strength and clarity, it suffers from poor processability. To overcome some of these disadvantages, Chapter 5 introduces methods to produce bimodal polyethylene resins using supported hybrid early and late transition metal catalyst systems. The presence of short chain branches in the higher molecular weight component is attributable to the incorporation of alpha-olefin molecules by the metallocene sites, while the nickel diimine catalyst sites produce chains with a distribution of…

► Metal dithiolenes [M(S2C2R2)n] have been studied for decades since their discovery due to their interesting spectroscopic, redox, biological and catalytic properties. S2C2(CF3)2-containing complexes have been…
(more)

▼ Metal dithiolenes [M(S2C2R2)n] have been studied for decades since their discovery due to their interesting spectroscopic, redox, biological and catalytic properties. S2C2(CF3)2-containing complexes have been studied but there is still much left unexplored due to the difficulty of obtaining the precursors and synthesizing the ligand. We present a synthetic method that uses easily obtained precursors and we built a relatively inexpensive apparatus to safely isomerize and react the gaseous intermediates.Molybdenum disulfide is used extensively in the petrochemical industry as catalyst for hydrodesulfurization of petroleum resources. We use dithiolenes to create homogenous structural model complexes of the proposed active sites of the molybdenum disulfide catalyst. We also experimentally determine competitive binding affinities for dihydrothiophene and tetrahydrothiophene, and explore some basic catalytic properties.Dithiolenes undergo reactions with alkenes to form new bonds. We present a new dithiolene reaction where it is attacked by a nucleophile (triphenylphosphine) to create a zwitterionic ligand as well as open an active site on a previously coordinatively saturated molybdenum tris(dithiolene). This technique is used to create a structural model complex for DMSO reductase and produce a pre-catalyst for that same reaction.After the determination that the actual catalyst for previously observed activity was a molybdenum bis-dithiolene complex, kinetic determination experiments were performed to elucidate the mechanism. Kinetic investigations suggest the binding of the phosphine oxide created from the use of triphenylphosphine as the oxygen acceptor competes with DMSO in the binding to the active site of the molybdenum bis(dithiolene). Additionally, the removal of oxygen from DMSO using the catalyst appears to involve a polar transition state.
Advisors/Committee Members: Fekl, Ulrich, Chemistry.

Nguyen, N. (2014). Reactions and Properties of Molybdenum Bis(dithiolene) Complexes Based on Bis(trifluoromethyl) Dithiolene and Labile Ligands. (Doctoral Dissertation). University of Toronto. Retrieved from http://hdl.handle.net/1807/68102

Nguyen N. Reactions and Properties of Molybdenum Bis(dithiolene) Complexes Based on Bis(trifluoromethyl) Dithiolene and Labile Ligands. [Doctoral Dissertation]. University of Toronto; 2014. Available from: http://hdl.handle.net/1807/68102

► Hydrogen fuel is a promising future energy carrier with many applications. Thermodynamically, 1.23 V is needed for the water electrolysis, which is a clean…
(more)

▼ Hydrogen fuel is a promising future energy carrier with many applications. Thermodynamically, 1.23 V is needed for the water electrolysis, which is a clean method to generate hydrogen gas. In practice excess potential is required, which is called overpotential, due to kinetic barriers. Catalysts to reduce the overpotential for the hydrogen evolution reaction (HER) include many homogeneous catalysts and heterogeneous catalysts. Heterogenization of homogeneous catalysts on electrode surfaces is an ideal way to study a catalyst by combining homogeneous and heterogeneous study together. In this dissertation, several characterization techniques have been employed, include cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, UV-visible spectroscopy, X-ray photoelectron spectroscopy, chronopotentiometry, and density functional theory. The heterogenization of the rhenium complex of the redox-active ligand 2-diphenylphosphinobenzenethiolate (ReL3)on glassy carbon electrode surfaces generated a stable modified electrode work for HER electrocatalysis in aqueous acidic condition with a relatively large overpotential. The cation form of ReL3, [ReL3]+ has been drop casted on the GC surface to prepare GC-[ReL3]+ which showed improved overpotential. Addition of a carbon black layer to generate GC-CB-ReL3 and GC-CB-[ReL3]+ decreased significantly the charge transfer resistance and overpotential for both catalysts. Tafel slope analysis for all electrodes indicates a Volmer rate determine step. The proposed mechanism is based on the homogeneous mechanism with support of DFT calculations. The redox active bis-thiosemicarbazone ligands ATSM and ATSP and their Cu- and Zn- derivatives were fabricated on GC surface as heterogeneous HER catalysts. The overpotential for the ATSM and ATSP ligands are 1.12 V and 1.09 V, while the overpotential for CuATSM and CuATSP are 774 mV and 745 mV, respectively. The Zn derivatives de-metallation during the electrolysis as observed by UV-vis spectroscopy and XPS analysis. Carbon paste electrodes (CPEs) have been used to improve the charge transfer resistance for the fabricated electrodes to achieve lower overpotential. The CPE-ReL3, CPE-ATSM and CPE-CuATSM electrodes were prepared and compared with GC electrodes. The CPE catalysts show significantly reduced overpotential compared to GC and the charge transfer resistance was decreased over 100 times relative to GC electrodes. Moreover, the CPEs exhibit excellent stability properties during the long-term electrolysis.
Advisors/Committee Members: Grapperhaus, Craig, Buchanan, Robert, Sumanasekera, Gamini, Zamborini, Francis.

► Electrochemical water splitting is a critical reaction for the conversion of renewable energy sources. It is limited by the oxygen evolution reaction (OER) which requires…
(more)

▼ Electrochemical water splitting is a critical reaction for the conversion of renewable energy sources. It is limited by the oxygen evolution reaction (OER) which requires high potentials to drive the reaction. The main drawback to OER catalysts is the trade-off between high activity at low potentials and stability over multiple uses. Ru metal has the lowest onset potential (∼1.3 V) and highest activity (100 - 4000 mA mg-1) due to the low energy barrier to Ru>4+ production that catalyses OER. Ru catalysts are limited by the immediate dissolution of the active species, resulting in catalysts that deteriorate in the first OER cycle.An OER electrode that delivers high activity at low potentials and remains active over multiple catalytic cycles remains a challenge. Synthesising a nanocatalyst with structural features that address both activity and stability separately offers a way to overcome this issue. This thesis focuses on creating nanoparticles with high electrochemically active surface areas made of low energy Ru surfaces. These can achieve both stability and activity by reducing the dissolution of Ru species from the highly accessible surfaces. Chapter 3 investigates the synthesis for Au-Ru branched nanoparticles with 3D branching and low index facets. By determining the key synthetic parameters to the formation of these structural features, a synthetic protocol is proposed. The growth of the Au-Ru branched nanoparticles is studied in chapter 4 using state-of-the-art transmission electron microscopy (TEM). The morphology and crystallography of intermediate nanoparticles are fully characterised to determine how these important structural features are formed. In chapter 5 the OER activity and stability of the Au-Ru branched nanoparticles are tested. Comparison to non-branched, non-faceted nanoparticles and TEM analysis of the nanoparticles after catalysis reveals the relationship between OER performance and structure. Chapter 6 investigates the synthesis of Pd-Ru bimetallic nanoparticles with core-shell and alloy structures as another means of achieving high electrochemically active surface areas and stable surfaces. By controlling synthetic variables a synthesis for nanoparticles with tunable size, shell thickness and composition is proposed for future optimisation as OER catalysts. Finally, conclusions are made across the synthesis, growth and OER performance of Ru-based bimetallic nanoparticles and opportunities for future work are proposed.
Advisors/Committee Members: Tilley, Richard, Chemistry, Faculty of Science, UNSW, Gooding, Justin, Chemistry, Faculty of Science, UNSW.

► Polymer electrolyte membrane fuel cells (PEMFCs) are attractive power sources of the future for a variety of applications including portable electronics, stationary power, and…
(more)

▼ Polymer electrolyte membrane fuel cells (PEMFCs) are attractive power sources of the future for a variety of applications including portable electronics, stationary power, and automobile application. However, sluggish cathode kinetics, high Pt cost, and durability issues inhibit the commercialization of PEMFCs. To overcome these drawbacks, research has been focused on alloying Pt with transition metals since alloy catalysts show significantly improved catalytic properties like high activity, selectivity, and durability. However, Pt-alloy catalysts synthesized using the conventional impregnation method exhibit uneven particle size and poor particle distribution resulting in poor performance and/or durability in PEMFCs. In this dissertation, a novel catalyst synthesis methodology is developed and compared with catalysts prepared using impregnation method and commercial catalysts. Two approaches are investigated for the catalyst development. The catalyst durability was studied under U. S. DRIVE Fuel Cell Tech Team suggested protocols. In the first approach, the carbon composite catalyst (CCC) having active sites for oxygen reduction reaction (ORR) is employed as a support for the synthesis of Pt/CCC catalyst. The structural and electrochemical properties of Pt/CCC catalyst are investigated using highresolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, while RDE and fuel cell testing are carried out to study the electrochemical properties. The synergistic effect of CCC and Pt is confirmed by the observed high activity towards ORR for the Pt/CCC catalyst. The second approach is the synthesis of Co-doped hybrid cathode catalysts (Co-doped Pt/CCC) by diffusing the Co metal present within the CCC support into the Pt nanoparticles during heat-treatment. The optimized Co-doped Pt/CCC catalyst performed better than the commercial catalysts and the catalyst prepared using the impregnation method in PEMFCs and showed high stability under 30,000 potential cycles between 0.6 and 1.0 V. To further increase the stability of the catalyst at high potential cycles (1.0-1.5 V), high temperature treatment is used to obtain graphitized carbon having optimum BET surface area. The novel catalyst synthesis procedure developed in this study was successfully applied for the synthesis of Co-doped Pt catalysts supported on the graphitized carbon which showed high activity and enhanced stability at high potentials.
Advisors/Committee Members: Branko Popov.

Jung, W. S. (2015). Development of Highly Active and Stable Hybrid Cathode Catalyst for PEMFCs. (Doctoral Dissertation). University of South Carolina. Retrieved from https://scholarcommons.sc.edu/etd/3261

Chicago Manual of Style (16th Edition):

Jung, Won Suk. “Development of Highly Active and Stable Hybrid Cathode Catalyst for PEMFCs.” 2015. Doctoral Dissertation, University of South Carolina. Accessed January 21, 2019.
https://scholarcommons.sc.edu/etd/3261.

► Light alkenes, such as propene and butenes, are important intermediates in the manufacture of fuel components and chemicals. The direct catalytic dehydrogenation of the corresponding…
(more)

▼ Light alkenes, such as propene and butenes, are important intermediates in the manufacture of fuel components and chemicals. The direct catalytic dehydrogenation of the corresponding alkanes is a selective way to produce these alkenes and is frequently carried out using chromia/alumina catalysts. The aim of this work was to obtain structure–activity information, which could be utilised in the optimisation of this catalytic system. The properties of chromia/alumina catalysts were investigated by advanced in situ and ex situ spectroscopic methods, and the activities were measured in the dehydrogenation of isobutane. The dehydrogenation activity of chromia/alumina was attributed to coordinatively unsaturated redox and non-redox Cr3+ ions at all chromium loadings. In addition, the oxygen ions in the catalyst appeared to participate in the reaction. The reduction of chromia/alumina resulted in formation of adsorbed surface species: hydroxyl groups bonded to chromia and alumina were formed in reduction by hydrogen and alkanes, and carbon-containing species in reduction by carbon monoxide and alkanes. Prereduction with hydrogen or carbon monoxide decreased the dehydrogenation activity. The effect by hydrogen was suggested to be related to the amount of OH/H species on the reduced surface affecting the number of coordinatively unsaturated chromium sites, and the effect by carbon monoxide to the formation of unselective chromium sites and carbon-containing species. The chromia/alumina catalysts were deactivated with time on stream and in cycles of (pre)reduction–dehydrogenation–regeneration. The deactivation with time on stream was caused mainly by coke formation. The nature of the coke species changed during dehydrogenation. Carboxylates and aliphatic hydrocarbon species formed at the beginning of the reaction and unsaturated/aromatic hydrocarbons and graphite-like species with increasing time on stream. The deactivation in several dehydrogenation–regeneration cycles was attributed to a decrease in the number of actives sites, which was possibly caused by clustering of the active phase into more three-dimensional structures. Acidic hydroxyl species of exposed alumina support may have contributed to the side reactions observed during dehydrogenation. Chromium catalysts prepared on unmodified alumina and on alumina modified with basic aluminium nitride-type species were compared in an attempt to increase the activity and selectivity in dehydrogenation. However, the presence of nitrogen in the catalyst was not beneficial for the dehydrogenation activity. A kinetic model was derived for the rate of dehydrogenation of isobutane on chromia/alumina. The dehydrogenation results were best described by a model with isobutane adsorption, possibly on a pair of chromium and oxygen ions, as the rate-determining step. Satisfactory description of the reaction rate depended upon inclusion of the isobutene and hydrogen adsorption parameters in the mathematical model. The activation energy of the rate-determining step was estimated to be…
Advisors/Committee Members: Helsinki University of Technology, Department of Chemical Technology, Laboratory of Industrial Chemistry.

▼ Monodisperse Pd nanocubes of 20 nm rib length and Pd
nanospheres of 3 nm diameter deposited on corundum were used as
efficient tool to reveal structure sensitivity of three-phase
hydrogenations of unsaturated alcohols. For an olefin alcohol
hydrogenation in the kinetic regime, surface (100) atoms of the
cubes displayed lower activity than other surface atoms of the
spheres. Apparent activation energies of 23 kJ/mol for the cubes
and 17 kJ/mol for the spheres confirmed the reaction structure
sensitivity. In an acetylenic alcohol hydrogenation, the cubes
showed higher selectivity to an olefinic product than the spheres.
Apparent activation energy was found as 38 kJ/mol for the cubes and
24 kJ/mol for the spheres. The apparent structure sensitivity in
this case was attributed to liquid-solid mass transfer limitations
governing the sphere-catalyzed reactions. The study shows the
applicability and limitations of the use of nanoparticles for
structure sensitivity studies in catalysis.

► Hydrotreating is the response to the necessity of a cleaner feed for downstream processes and reduced pollution. Hydrotreating catalysts are vital in this process; hence…
(more)

▼ Hydrotreating is the response to the necessity of a
cleaner feed for downstream processes and reduced pollution.
Hydrotreating catalysts are vital in this process; hence catalyst
deactivation is a key issue. The principal objective of this
research was the experimental study of hydrotreating catalyst
deactivation due to arsenic compounds. The hydrotreating of light
gas oil, in the presence and absence of an arsenic compound over a
commercial NiMoS catalyst, was investigated in a trickle bed
reactor (temperature 315-360˚C, space velocity = 1-3 h-1, pressure
= 3MPa). Kinetics of first order for nitrogen and sulphur were
found and activation energies values of 32 kj/mol and 76 kj/mol
respectively. Studies of activity changes, suggested that arsenic
mainly affects the conversion of sulfur compounds; which might
indicate that arsenic prefers mainly the S edge of the catalysts.
Activation energy values decreased after arsenic introduction,
which may suggest pore plugging of the catalyst.

► Using data from artificial gas mixtures, global kinetic models for a platinum diesel oxidation catalyst are developed. The modelling of CO and C3H6 was inspired…
(more)

▼ Using data from artificial gas mixtures, global
kinetic models for a platinum diesel oxidation catalyst are
developed. The modelling of CO and C3H6 was inspired by the
classical work of Voltz et al.[1], while the modelling of NO and
C3H6 was based on the earlier work of Pandya[2], Mulla et al.[3],
Bhatia et al.[4] and Hauff et al.[5]. The creation of the model was
performed piecewise, starting from experiments on single reactants.
A new model is proposed to account for the formation of N2O. A
global model is developed that is able to correlate with reasonable
accuracy the results from the complete gas mixture. The model is
not, however, able to correlate all of the data from feeds
containing the complete set of reactants and those with single or
dual reactants present.

▼ Novel anode catalysts have been developed for sour
natural gas solid oxide fuel cell (SOFC) applications. Sour natural
gas comprises light hydrocarbons, and typically also contains H2S.
An alternative fuel SOFC that operates directly on sour natural gas
would reduce the overall cost of plant construction and operation
for fuel cell power generation. The anode for such a fuel cell must
have good catalytic and electrocatalytic activity for hydrocarbon
conversion, sulfur-tolerance, resistance to coking, and good
electronic and ionic conductivity. The catalytic activity and
stability of ABO3 (A= La, Ce and/or Sr, B=Cr and one or more of Ti,
V, Cr, Fe, Mn, or Co) perovskites as SOFC anode materials depends
on both A and B, and are modiﬁed by substituents. The materials
have been prepared by both solid state and wet-chemical methods.
The physical and chemical characteristics of the materials have
been fully characterized using electron microscopy, XRD,
calorimetry, dilatometry, particle size and area, using XPS and
TGA-DSC-MS. Electrochemical performance was determined using
potentiodynamic and potentiostatic cell testing, electrochemical
impedance analysis, and conductivity measurements. Neither
Ce0.9Sr0.1VO3 nor Ce0.9Sr0.1Cr0.5V0.5O3 was an active anode for
oxidation of H2 and CH4 fuels. However, active catalysts comprising
Ce0.9Sr0.1V(O,S)3 and Ce0.9Sr0.1Cr0.5V0.5(O,S)3 were formed when
small concentrations of H2S were present in the fuels. The
oxysulﬁdes formed in-situ were very active for conversion of H2S.
The maximum performance improved from 50 mW cm−2 to 85 mW cm−2 in
0.5% H2S/CH4 at 850 °C with partial substitution of V by Cr in
Ce0.9Sr0.1V(O,S)3 . Selective conversion of H2S offers potential
for sweetening of sour gas without affecting the hydrocarbons.
Perovskites La0.75Sr0.25Cr0.5X0.5O3−δ, (henceforth referred to as
LSCX, X=Ti, Mn, Fe, Co) are active for conversion of H2, CH4 and
0.5% H2S/CH4. The order of activity in the different fuels depends
on the substituent element: CH4, X=Fe>Mn>Ti; H2,X =
Fe>Mn>Ti; and 0.5% H2S/CH4, X =
Fe>Ti>Mn. The electrocatalytic activity for methane
oxidation in a fuel cell correlates with ex-situ temperature
programmed catalytic activity. A process is proposed to explain the
difference in catalyst order and enhanced activities in H2S/CH4 as
fuel compared to CH4 alone. The maximum power density of 250 mW
cm−2 was attained using a fuel cell with a composite anode,
LSCFe-GDC | YSZ(0.3 mm) | Pt, operated at 850 °C (GDC is
Ce0.9Gd0.1O3, a good mixed conductor under reducing
conditions).

► Platinum (Pt) alloy nanoparticles are used as catalysts in electrochemical cells to reduce oxygen to water and to oxidize hydrogen; the overall reaction converts chemical…
(more)

▼ Platinum (Pt) alloy nanoparticles are used as catalysts in electrochemical cells to
reduce oxygen to water and to oxidize hydrogen; the overall reaction converts chemical
energy into electrical energy. These nanocatalysts are deposited on a carbon substrate
and their catalytic function takes place in acid medium. This harsh environment causes
an undesired reaction, which is the dissolution of the metal atoms into the acid medium;
thus affecting the catalyst life. This dissertation aims to investigate the dissolution
mechanism of fuel cell cathode catalysts at the atomic level starting from the oxygen
reaction intermediates on the cathode catalyst surface and propose guidelines to improve
cathode catalysts durability based on our proposed mechanism. Density functional
theory is employed to study various possible scenarios with the goals of understanding
the mechanism of the metal atom dissolution process and establishing some guidelines
that permit a rational design of catalysts with better stability against dissolution. A
thermodynamic analysis of potential metal dissolution reactions in acid medium is
presented first, using density functional theory calculations to explore the relative
stabilities of transition metals in relation to that of Pt. The study is performed by
comparing the change in reaction Gibbs free energies for different metals in a given
dissolution reaction. Then, a series of density functional theory studies, tending to
investigate the adsorbed atomic oxygen absorption process from cathode catalyst surface
into its subsurface, includes: 1) the oxygen adsorption on various catalyst surfaces and
oxygen absorption in subsurface sites to figure out the minimum energy pathway and
energy barrier of on-surface oxygen migration and absorption into subsurface; 2) the oxygen coverage, the other oxygen reduction reaction intermediates, and water effects
on the oxygen absorption process according to reaction pathways, energy barriers, and
thermodynamic analysis; 3) the oxygen absorption process on several Pt-based alloys
with various compositions and components to find out the best alloy to inhibit atomic
oxygen absorption including both kinetic and thermodynamic analyses, and the effects
of such alloyed species on the inhibition process.
Advisors/Committee Members: Balbuena, Perla B (advisor), Seminario, Jorge M (committee member), Soriaga, Manuel P (committee member), Ugaz, Victor M (committee member).

► A new protocol for direct amination of N-Methyl-2-phenylindole catalyzed by copper(II) trifluoromethanesulfonate was presented. Both of (E)-N-(1,1'-Dimethyl-2,2' -diphenyl-2,3'-biindolin-3-ylidene)-4-methylbenzenesulfonamideï¼4ï¼and 4-methyl -N-(1-methyl-2-phenyl-1H-indol-3-yl)benzenesulfonamideï¼2ï¼were obtained under the optimal reaction…
(more)

► Polyolefins comprise the majority of the world's plastics consumption. Polyethylene and polypropylene are the two most widely utilized materials due to their exceptional properties and…
(more)

▼ Polyolefins comprise the majority of the world's plastics consumption. Polyethylene and polypropylene are the two most widely utilized materials due to their exceptional properties and their inexpensive monomer feedstock. However, the polymers' true success derives from the heterogeneous catalysts that produce them. The discovery of these catalysts by Ziegler and Natta in the mid 20th century allowed for the linearity of polyethylene and the regio- and stereoregularity of polypropylene to be inherent in the microstructures. Additionally, the catalysts' simplicity and effectiveness are what make them the primary method for the commercial synthesis of polyolefins. The homogenous analogues of the Ziegler-Natta catalysts have given researchers the opportunity to tailor the properties of the polyolefins even further. Early group metal catalysts have been prominently studied due to their similarity to the heterogeneous systems. However, the arrival of late-transition metal catalysis for olefin polymerization delivered the ability to control microstructures in new ways as well as tolerate functionality. This work describes the investigations into the development of new nickel-mediated processes for the polymerization of olefins. Nickel (II) !-diimine catalysts have been previously developed for the regioregular "-2 enchainment of !-olefins. However, controlling the tacticity has proven to be quite difficult. Chapter two describes work toward further controlling the stereoselectivity of these catalysts to produce "-2 enchain poly(!-olefins) with high isotacticity, and in the case of 1-butene, a new class of semi-crystalline polyolefins. Ligand sterics and electronics aid in the elucidating mechanistic insight into this unique polymerization. Chapter three regards the development of an open geometry neutral nickel catalyst exhibiting high activity in ethylene polymerizations. The presence of bulky substituents on an amidinate ligand protects the axial sites of an active square-planar nickel center from associative displacement of a growing polymer chain, producing higher molecular weight polymer with greater activities than previously reported catalysts of this type. The addition of copper (II) bromide further enhances the activity of the catalyst by producing higher turnovers and achieving a much more narrow molecular weight distribution. Possible explanations for the copper's effect are discussed.
Advisors/Committee Members: Lewis, Chad Arthur (committeeMember), Dichtel, William Robert (committeeMember).

► This thesis explores both the optical and catalytic properties of cubic shaped nanoparticles. The investigation begins with the sensing capabilities of cubic metal dimers. Of…
(more)

▼ This thesis explores both the optical and catalytic properties of cubic shaped nanoparticles. The investigation begins with the sensing capabilities of cubic metal dimers. Of all the plasmonic solid nanoparticles, single Ag or Au nanocubes exhibit the strongest electromagnetic fields. When two nanoparticles are in close proximity to each other the formation of hot spots between plasmonic nanoparticles is known to greatly enhance these electromagnetic fields even further. The sensitivity of these electromagnetic fields as well as the sensitivity of the plasmonic extinction properties is important to the development of plasmonic sensing. However, an investigation of the electromagnetic fields and the corresponding sensing capabilities of cubic shaped dimers are currently lacking.
In Chapters 2-5 the optical properties of cubic dimers made of either silver or gold are examined as a function of separation distance, surrounding environment, and dimer orientation. A detailed DDA simulation of Au–Au and Ag-Ag dimers oriented in a face-to-face configuration is conducted in Chapter 2. In this Chapter a distance dependent competition between two locations for hot spot formation is observed. The effect of this competition on the sensing capabilities of these dimers is further explored in Chapters 3 and 4. This competition originates from the generation of two different plasmonic modes. Each mode is defined by a unique electromagnetic field distribution between the adjacent nanocubes.
In Chapter 4 the maximum value of the electromagnetic field intensity is investigated for each mode. Notably the magnitude of the electromagnetic field is not directly proportional to its extinction intensity. Furthermore, the sensitivity of a plasmonic mode does not depend on its extinction intensity. The sensitivity is rather a function of the magnitude of the electromagnetic field intensity distribution. Also, the presence of a high refractive index substrate drastically affects the optical properties and subsequent sentivity of the dimer. In Chapter 5 the sensing properties of a cubic dimer is investigated as a function of orientation. As the separation distance of the nanocube dimer is decreased the orientation of the dimer drastically affects its coupling behavior. The expected dipole-dipole exponential coupling behavior of the dimer is found to fail at a separation distance of 14 nm for the edge-to-edge arrangement. The failure of the dipole-dipole coupling mechanism results from an increased contribution from the higher order multipoles (eg. quadrupole-dipole). This behavior begins at a separation distance of 6 nm for the face-to-face dimer. As a result, the relative ratio of the multipole to the dipole moment generated by the edge-to-edge dimer must be larger than the ratio for the face-to-face orientation.
In the last section of this thesis the catalytic properties of cubic nanoparticles composed of a platinum-silver alloy are investigated. The catalytic activity and selectivity towards a given reaction is intimately related to the…
Advisors/Committee Members: Zhang, Z. J. (advisor), Jones, Christopher W. (committee member), Sadighi, Joseph P. (committee member), Wine, Paul H. (committee member).

► This research presents a multi-scale analysis of the transport and reaction processes in the catalyst coating of a reformer to optimize the catalyst coating microstructure…
(more)

▼ This research presents a multi-scale analysis of the transport and reaction processes in the catalyst coating of a reformer to optimize the catalyst coating microstructure for methane steam reforming. A multi-scale methodology is developed to incorporate and analyze the effect of the catalyst coating morphology on the performance of a wall-coated reformer, based on hypothetical catalyst structures generated using an in-house particle packing code. The results show the significant effect of intra-particle and inter-particle porosity as well as particle size on the rate of hydrogen production in the coating. This study also shows that an optimal catalyst coating has decreasing porosity along the reformer length based on the difference in the degree of diffusion limitation. The results of the multi-scale analysis based on random particle packing are compared with the analysis based on the real catalyst coating pore structure obtained from nano- and micro-computed tomography. The comparison shows that despite similar morphological characteristics and transport properties, the rate of hydrogen production in the packing of overlapping spheres is higher than the rate in the real catalyst structure. This result also shows that by making a structured catalyst coating with a tailored pore network, the performance of the coating improves significantly. Based on the assumption that a structured catalyst coating can be represented by a random packing of spheres, a systematic parametric study is done using response surface methodology and Latin hypercube design of experiment to optimize the catalyst coating microstructure.

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Tanhatan Naseri SA. COMPUTATIONAL ANALYSIS OF THE REACTING FLOW IN THE CATALYST COATING OF A REFORMER USING A MULTISCALE APPROACH
. [Thesis]. Queens University; 2015. Available from: http://hdl.handle.net/1974/13483

Note: this citation may be lacking information needed for this citation format:Not specified: Masters Thesis or Doctoral Dissertation

Université Catholique de Louvain

19.
de Crane d'Heysselaer, Simon.
Hybrid heteropolyacid-terpyridine heterogeneous catalysts for the epoxidation of olefins with H2O2.

► Epoxide compounds are widely used in the chemical industry to produce resins, paints, surfactants and as intermediates in organic synthesis. Nowadays, epoxides are commonly synthesized…
(more)

▼ Epoxide compounds are widely used in the chemical industry to produce resins, paints, surfactants and as intermediates in organic synthesis. Nowadays, epoxides are commonly synthesized through methods that generate a vast amount of unwanted by-products and by using reactants which contain certain environmental risks. Therefore, the exploration of a new catalytic strategies is imperative in order to overcome these issues. Olefins epoxidation by heterogeneous catalysts has shown to be an attractive strategy with interesting advantages in terms of efficiency and catalyst reusability, when combined with hydrogen peroxide as a green epoxidizing agent. In this light, polyoxometalate (POM) compounds have proven to be interesting candidates for a wide variety of oxidation reactions thanks to their versatile acidic and redox properties. However, achieving high olefin conversions and epoxide selectivities while working in heterogeneous conditions still remains a challenge. This challenge could be circumvented by forming an appropriate polyoxometalate hybrid catalyst using hydrophobic organic ligands to optimize the catalytic performance and thus work in heterogeneous conditions. The organic ligands chosen for this study are terpyridines and phosphotungstic acid was chosen as POM. The nitrogen atoms of these terpyridines act as Lewis bases and form H-bonds with the POM terminal oxygens and effectively form solid organic-inorganic hybrids. The final objective of the studies surrounding this master’s thesis is to effectively develop hybrid catalysts based on polyoxometalates which present high activities and a significant selectivity towards epoxides in the epoxidation reactions of olefins in heterogeneous conditions. To do so, different terpyridine ligands were initially synthesized through a well-known synthesis route, with different functional groups attached to it. These terpyridines were then successfully linked to the Keggin structure of phosphotungstic acid H3PW12O40 to form the final hybrid catalyst. The catalysts were tested in the epoxidation reaction of cyclooctene using H2O2 as oxidizing agent in an acetonitrile solvent. However, even though the hybrid catalysts showed lower conversions than the homogeneous pristine II H3PW12O40, which has been investigated in previous studies, higher selectivities towards cyclooctane epoxide were found. Studies about the reaction mechanism of H3PW12O40 type heteropolyacids indicated that the active species in the epoxidation mechanism was the peroxo PW4O243- species. Therefore, in order to achieve better catalytic performances, H3PW12O40 was pre-activated with H2O2 before hybridization. This way, the new peroxo hybrid obtained presented much better conversion and selectivity numbers. This study leads to the conclusion that the newly synthesized peroxotungstate hybrid compound, is the responsible for the high catalytic activity in the epoxidation reaction. Hence, more research in this matter should be done to have a better understanding of the catalyst behaviour, and notably by…
Advisors/Committee Members: UCL - Faculté des bioingénieurs, Gaigneaux, Eric M., Elias, Benjamin.

► The effective utilization of CO2 as a renewable raw material for the production of useful chemicals is an area of great interest. In particular, the…
(more)

▼ The effective utilization of CO2 as a renewable raw material for the production of useful chemicals is an area of great interest. In particular, the catalytic conversion of CO2 into cyclic carbonates, which are useful chemical intermediates employed for the production of plastics and organic solvents, represents an attractive route for the efficient use of carbon dioxide. Microporous crystals, including zeolites and metal organic frameworks (MOFs), and mesoporous ordered oxides possess many desirable properties, which make them appealing for cycloaddition reactions. In general, these porous materials display chemical and thermal stability, moderate to high CO2 uptakes, an open porous structure for improved mass transfer, accessible pore volumes, acid sites which are known as active sites for cycloaddition reactions, high surface areas. SAPOs (silicoaluminophosphates), a particular type of small pore molecular sieves, have received considerable interest because of their applications in separations, catalysis, and adsorption. Their unique functional properties are associated with their chemical and thermal stability, unique shape selectivity, molecular sieving properties, ordered microporous crystalline structure, and surface properties. SAPO-56 is a crystalline microporous silicoaluminophosphate in which silicon substitutes for some of the phosphorous and aluminum atoms in the structural framework. The AFX topology of SAPO-56 is characterized by a three dimensional structure with pore cages arranged in interconnected networks, with window (pore size) sizes of ~3.4×3.6 Å. Due to its pore size similar to the kinetic diameter of several relevant gas molecules such as CO2, CH4, O2, N2 as well as due to relatively high CO2 uptakes, SAPO-56 may find potential applications for CO2 conversion to useful chemicals. A conventional hydrothermal synthesis approach used to synthesize SAPO-56 requires typically long synthesis times (days) and relatively high hydrothermal temperatures (200 °C). Microwave heating offers several advantages over conventional heating, such as fast crystallization, phase selectivity, narrow particle size distribution, abundant nucleation, morphology and size control and rapid and uniform heating. Herein we present the synthesis of SAPO-56 crystals via microwave heating. The resultant crystals displayed high catalytic activity in the synthesis of chloropropene carbonate from CO2 and epichlorohydrin. The Microwave as-synthesized SAPO-56 displayed crystal size as ~3-4 µm, while the crystal size hydrothermal as-synthesized SAPO-56 is ~50 µm. When 3-4 µm crystals were used, the yield to chloropropene carbonate was 84.8%, whereas the yield to the carbonate was only 42.2% when crystals of about 50 µm were used. The enhanced catalytic activity of SAPO-56 crystals was related to their high CO2 adsorption capacity, small crystal size, and the presence of acid sites. In addition, silica nanospheres present in the surface of the smaller SAPO-56 crystals may display a role as specific surface sites for the…
Advisors/Committee Members: Carreon, Moises A..

Xie, Zhenzhen, 1. (2013). Microwave-assisted synthesized SAPO-56 as a catalyst in the conversion of CO2 to cyclic carbonates. (Masters Thesis). University of Louisville. Retrieved from 10.18297/etd/1602 ; https://ir.library.louisville.edu/etd/1602

Chicago Manual of Style (16th Edition):

Xie, Zhenzhen, 1988-. “Microwave-assisted synthesized SAPO-56 as a catalyst in the conversion of CO2 to cyclic carbonates.” 2013. Masters Thesis, University of Louisville. Accessed January 21, 2019.
10.18297/etd/1602 ; https://ir.library.louisville.edu/etd/1602.

Xie, Zhenzhen 1. Microwave-assisted synthesized SAPO-56 as a catalyst in the conversion of CO2 to cyclic carbonates. [Masters Thesis]. University of Louisville; 2013. Available from: 10.18297/etd/1602 ; https://ir.library.louisville.edu/etd/1602

► The increased interest in finding alternative transportation fuel sources to fossil fuels has led to significant research interest on different types of renewable sources. Biodiesel…
(more)

▼ The increased interest in finding alternative
transportation fuel sources to fossil fuels has led to significant
research interest on different types of renewable sources.
Biodiesel continues to grow as a sound substitute for petro-diesel,
and it can used either as 100 percent biodiesel or a blend of
biodiesel and diesel, without major modifications to the diesel
engine. Biodiesel is made by reacting vegetable oil and alcohol, in
the presence of a catalyst to produce fatty acid alkyl esters
(biodiesel) and glycerol. As research continues, special attention
has been paid to improve the biodiesel production process, whether
in the improvement of the feedstocks, catalysts, or reaction
conditions. The conventional method of producing biodiesel utilizes
homogenous catalysts which require the use of water to wash away
the catalysts at the end of the reaction, leading to the generation
of wastewater. Since biodiesel is considered an environmentally
friendly alternative to petro-diesel, it is important to minimize
the generation of wastewater as much as possible. One way to reduce
the amount of wastewater that is generated is by the use of
heterogeneous catalysts rather than homogenous catalysts.
Heterogeneous catalysts can potentially eliminate the need of the
water-washing step associated with the conventional method of
making biodiesel. The objective of this work was to produce
biodiesel using activated carbon-supported sodium hydroxide as the
heterogeneous catalyst without water-wash. The goal was achieved,
as biodiesel was produced. Fourier Transform Infrared Spectroscopy
was used to identify the biodiesel sample that was produced. The
biodiesel conversion was 99.3%, however the quality of the
biodiesel was an issue. The kinematic viscosity was 4.45, which is
within ASTM standards, but the free and bound glycerin in the
product exceeded the standard amount allowed. The bound glycerin
was attributed to the incomplete conversion of the triglyceride
molecule. The water content in the sample also exceeded the
acceptable amount. The ASTM standard for water content is 500ppm
but the product contained 888ppm. Therefore, even though the
catalyst used shows promise as effective in the goal of eliminating
water-wash, an optimization of the process is needed in order to
produce biodiesel that meets standards. Conditions such as
temperature, catalyst amount, and methanol amount, which can affect
the conversion and quality of the product, need to be optimized.

► This dissertation focuses on fundamental understanding of the roles of supports and noble metals in the sulfur-tolerant catalysts for low-temperature hydrogenation of aromatics in the…
(more)

▼ This dissertation focuses on fundamental understanding
of the roles of supports and noble metals in the sulfur-tolerant
catalysts for low-temperature hydrogenation of aromatics in the
presence of sulfur. Emphasis was placed on investigating the effect
of supports and supported metals for high sulfur tolerance and
verifying a catalyst design concept for the sulfur-tolerant noble
metal catalyst based on shape selective exclusion of sulfur and
hydrogen spillover for low- temperature hydrogenation of aromatics
[C.S. Song, Chemtech, 29 (1999) 26-30]. The hybrid
zeolite-supported Pd catalyst was prepared to improve sulfur
tolerance, based on the proposed catalyst design concept. The
hybrid catalyst consists of Pd supported on Y and A type zeolites.
For further investigation on small pore system in hybrid catalyst,
surface metal passivation by silica coating and pore size control
by potassium ion exchange were employed to zeolite A-supported Pd
catalyst. Although Pd on Zeolite A showed no catalytic activity for
hydrogenation of tetralin, adding the small-pore catalyst to Pd/Y
significantly enhanced sulfur tolerance of the catalyst for both
naphthalene and tetralin hydrogenation in the presence of sulfur in
the form of benzothiophene. Sulfur tolerance of the hybrid catalyst
is mainly attributed to the small pore system, inducing
size-selective exclusion of bulky sulfur compounds as well as
hydrogen spillover from metal inside small pore component. Hydrogen
spillover plays two roles in maintaining high sulfur tolerance of
the hybrid catalyst: first, regeneration of sulfur-poisoned metal
active sites in the large pores of Pd/Y as well as
hydrodesulfurization of aromatic sulfur compounds over the zeolite
Y support. On the basis of the above results and discussion
focusing on the importance of the supports and metal types for
improving sulfur tolerance, the hybrid catalyst system based on the
new design concept of sulfur tolerant catalyst is effective in the
development of sulfur tolerant catalysts for low-temperature
hydrogenation of aromatics.

► A significant amount of research has been dedicated towards the study and improvement of catalysts. A better understanding of how catalysts work can lead to…
(more)

▼ A significant amount of research has been dedicated
towards the study and improvement of catalysts. A better
understanding of how catalysts work can lead to developing more
cost-efficient catalytic systems for a variety of applications. My
research is focuses on catalytic systems used in three different
fields, which are (i) organometallic polymerization catalysts, (ii)
molecular motors and (iii) biomass conversion. Researchers have
long studied and modified organometallic catalysts for use in the
direct co- and homopolymerization of monomers with polar functional
groups. The ability to add polar moieties to polymers, which can
potentially yield materials with a wider range of physical
properties, is highly desirable. In this study (i), a series of
naphthoxyimine palladium(II) catalysts – in which the naphthyl
backbone had been functionalized with different moieties – were
synthesized and systematically studied to determine the ligand
structure’s impact on catalytic activity. The study showed that
slight modifications of the naphthyl backbone led to significant
changes in the polymer’s molecular weight and polydispersity index.
The catalysts were also displayed some ability to co-polymerize
ethylene and functionalized norbornene. These positive results
suggest that further exploration of naphthoxyimine palladium (II)
catalysts may be fundamentally interesting. The effect of active,
motile particles at the nanoscale has been vigorously researched
during the past decade. By understanding how such active
suspensions behave, researchers can gain new insights which can
potentially provide new applications in many fields. Here (ii) the
momentum transfer of active catalysts (Grubbs’ 2nd generation
catalyst with a hydrodynamic radius of 6Å) to their immediate
surroundings is observed in an organic suspension. This phenomenon,
which has been coined “enhanced diffusion,” has not been well
studied at the angström scale until now. Diffusion-NMR spectroscopy
surprisingly revealed that these angström sized catalysts nearly
double the speed of diffusion of passive molecular tracers in their
immediate surroundings. This result is particularly intriguing
because in this size regime, the viscosity of the surroundings is
expected to completely overcome the inertial forces of these
catalysts. This study has prompted further diffusion-NMR studies of
molecular catalysts and enzymes as molecular motors. Catalytic
systems play a crucial role in the conversion of renewable
biomasses into energy and useful materials. This field of research
has become increasingly important and lucrative as fossil fuel
sources continue to decline/destabilize in the face of increased
worldwide demand for more resources. In this work (iii), the
efficacy of a hydrogen-pressurized, biphasic catalytic system to
convert linear sugar polyols to iodoalkanes was examined. These
iodoalkanes can easily be converted to 1-alkenes which can then be
used for the synthesis of low density polyethylene. The results
indicated that the system products were relatively pure and…

► Direct methanol fuel cell (DMFC) is an attractive power source for portable applications in the near future, due to the high energy density of liquid…
(more)

▼ Direct methanol fuel cell (DMFC) is an attractive
power source for portable applications in the near future, due to
the high energy density of liquid methanol. Towards
commercialization of the DMFC, several technical and economic
challenges need to be addressed though. The present study aims at
developing and characterizing high performance membrane electrode
assemblies (MEAs) for the DMFCs by using a hydrocarbon type
membrane (PolyFuel 62) and supported catalysts (PtRu/C). First,
methanol and water transport properties in the PolyFuel 62 membrane
were examined by various material characterization methods.
Compared with the currently used perflurosulfonated Nafion 212
membrane, the PolyFuel membrane has lower methanol crossover,
especially at high testing temperature. In addition, based on
results of water diffusivity test, water diffusion through the
PolyFuel membrane was also lower compared with the Nafion membrane.
In order to check the possible impacts of the low methanol and
water diffusivities in the PolyFuel membrane, a MEA with this new
type of membrane was developed and its performance was compared
with a Nafion MEA with otherwise identical electrodes and GDLs. The
results showed anode performance was identical, while cathode
performance of the PolyFuel MEA was lower. More experiments
combined with a transmission line model revealed that low water
transport through the PolyFuel membrane resulted in a higher proton
resistance in the cathode electrode and thus, leading to a low
cathode performance. Thus increasing the water content in the
cathode electrode is critical for using the PolyFuel membrane in
the DMFC MEA. Then, a low loading carbon supported catalyst,
PtRu/C, was prepared and tested as the anode electrode in a MEA of
the DMFC. Compared with performance of an unsupported MEA, we could
find that lower performance in the supported MEA was due to
methanol transport limitation because of the denser and thicker
supported catalyst layer. Accordingly, an addition of a pore
former, Li2CO3, was proposed during the catalyst ink preparation.
This was proved to be very effective, largely improving anode
performance with only 1/3 of catalyst loading. Finally, the
PolyFuel membrane and supported catalysts were ready to be applied
in the new MEA for the DMFCs. The new made MEA, with the catalyst
loading of 2.6-time lower than a reference MEA, showed a very
promising result, about only 10mV performance loss under the
current density of 150mA/cm2 compared with the reference MEA.
Moreover, a short-term decay test indicated that the new MEA may
have better durability and life because of its low methanol
crossover on the cathode electrode due the PolyFuel
membrane.

Organic molecules as reaction catalysts (organocatalysts) has represented a major direction of research over the past 10-15 years. Organoboron compounds possess many advantageous features of…
(more)

▼

Organic molecules as reaction catalysts (organocatalysts) has represented a major direction of research over the past 10-15 years. Organoboron compounds possess many advantageous features of organocatalysts, including their relatively low cost and toxicity, their high functional group tolerance and ease of structural modification. 2H-Chromenes have been studied extensively as a consequence of their widespread natural occurrence, diverse biological properties and photochromic behaviour. They have been employed as useful intermediates in the synthesis of many natural products, pharmaceuticals and photochromic ophthalmic plastic lenses. Chapter 1 describes the optimization and initial substrate scope of an arylboronic acid-catalyzed synthesis of 2H-chromenes from the condensation of various phenols and aldehydes. Chapter 2 explores the utility of borinic acid catalysts in a Conia-Ene reaction. Finally, Chapter 3 discusses the synthesis of homobarrelenones, attractive building blocks for organic synthesis, via a Diels-Alder cycloaddition reaction using catalytic boronic acids.

► Ethanol and higher alcohols can be used as a fuel or fuel additive in gasoline engines as well as a hydrogen carrier. One of the…
(more)

▼ Ethanol and higher alcohols can be used as a fuel or fuel additive in gasoline engines as well as a hydrogen carrier. One of the promising methods to synthesize these alcohols is based on thermochemical conversion of CO and H2 (CO hydrogenation). Conventional catalysts used for the conversion CO and H2 (syngas) to ethanol typically give yields less than 20% with the balance resulting mostly in the formation of the thermodynamically favored products CH4 and CO2. New catalysts with compositions designed to kinetically favor the formation of ethanol and higher alcohols are needed. Electrodeposition of nanowires offers a means to control the surface properties of multimetallic catalysts in a way that is not possible with conventional catalyst preparation methods such as co-precipitation and impregnation. A principle advantage of electrodeposition over conventional methods centers on its ability to control the active metal environment at the atomic level. In this work, Cu-ZnO and Mn-Cu-ZnO novel nanowire/tube catalysts have been prepared by electrodeposition using a template synthesis technique. To the best of our knowledge, electrodeposited Cu-based nanowires have never been used as heterogeneous catalysts. Different current and pulsed current schemes were used to control composition and morphology of the resulting nanowire/tube catalysts. Pulse waveforms with suitable on-time (cathodic current) and off-times (no current) were used to tailor the atomic environment of the nanowire catalysts. A fixed bed tubular reactor was used to synthesize alcohols from CO and H2 (syngas). In addition to C2-C4 alcohols products of interest, methanol, methane, propylene, and CO2 were the main side products at various reaction conditions. The reaction was performed at varying temperature (250C-310C), pressure (10-20 bar), H2/CO ratio (1-3), and GHSV (7,500-33,000 scc/h-gcat). The addition of Mn to the Cu-ZnO catalyst increased the selectivity toward ethanol and higher alcohols by reducing methanation. Schulz-Flory distributions of the products suggest that the synthesis of alcohols and hydrocarbons require different sites.

► My research is focused on two main objectives, the study of catalytic efficiency and mechanism of palladium nanoparticles stabilized by poly(vinylpyrrolidone) (PVP) for carbon-carbon coupling…
(more)

▼ My research is focused on two main objectives, the study of catalytic efficiency and mechanism of palladium nanoparticles stabilized by poly(vinylpyrrolidone) (PVP) for carbon-carbon coupling reactions, and to rationally synthesize metal nanoparticles stabilized by metal-carbon bonds and apply them to catalyze carbon-carbon coupling reactions.
In the first project, Pd nanoparticles stabilized by PVP were used to catalyze carbon-coupling reactions, specifically the Stille and Suzuki reactions. The mechanism of carbon-carbon coupling reactions was studied. The uncertainty of whether nanoparticles or Pd salts are the catalyst was also examined using the same experimental procedure with Pd salts to examine their catalytic activity in carbon-carbon coupling reactions. Results show that the presence of O2 is crucial to the Stille reaction with the Pd nanoparticles, which are nearly completely inert under N2, while the K2PdCl4 precursor is itself quite active for the Stille reaction. However, the Pd nanoparticles were found to be active for the Suzuki reaction with high yields in the absence of O2. The yields for 4-chlorobenzoic acid are higher than 4-bromobenzoic acid and occur for un-catalyzed reactions, for reasons that are still unknown. Finally Au nanoparticles have been tested by the same experimental procedure and have no catalytic activity for these two reactions.
In the second project, the synthesis of Au and Pd monolayer protected clusters (MPCs) with metal carbon covalent linkages was examined, and the stability of the resulting MPCs was tested. UV-Vis spectra and TEM images show the formation of Au and Pd nanoparticles and 1H NMR was used to characterize the ligands attached to the surface of the nanoparticles. The decylphenyl-stabilized Pd MPCs were synthesized successfully and quite stable in air, while decylphenyl-stabilized Au MPCs prepared with the same protocol have less stability and are easily decomposed. XPS spectra indicate the composition of decylphenyl-stabilized Pd MPCs is a combination of Pd0 and Pd2+ species with the Pd2+ species in excess. In addition, alkylphenyl-stabilized Pd nanoparticles were shown to be effective catalysts for carbon-carbon coupling reactions such as Suzuki and Stille reactions as well as hydrogenation reactions. Finally, it was noted that Pd-C bonds could be easily reduced by H2 when performing hydrogenation reactions resulting in nanoparticle aggregation and precipitation under hydrogenation conditions.
Advisors/Committee Members: Scott, Robert W. J., Foley, Stephen, Sanders, David A. R., Soltan, Jafar.

► Metal alkoxide and hydroxides are popular and inexpensive base catalysts used by industry to produce fatty acid esters. However hydroxides produce water when dissolved in…
(more)

▼ Metal alkoxide and hydroxides are popular and inexpensive base catalysts used by industry to produce fatty acid esters. However hydroxides produce water when dissolved in an alcohol based solvent. Consequently the water molecule releases hydroxide anion, which attacks triglyceride to produce free fatty acids instead of fatty acid methyl ester. Presence of free fatty acid is highly unfavorable because it reacts with the base catalyst to produce soap and hence, inactivates the catalyst. The alternative, alkoxide, is therefore, a preferred choice over hydroxide. Nevertheless, alkoxides are more expensive, their production is hazardous and they are dangerous to transport. In this study, low cost sodium alkoxide base catalysts were synthesized from 50 wt% sodium hydroxide solution and non-volatile, non-toxic polyols using an alternative route which is less expensive and hazardous. Gravimetric analysis showed that polyols effectively aid in evaporation of 50 wt% aqueous sodium hydroxide during formation of alkoxide compounds. The resulting products are strong base compounds, which were characterized using single crystal, X-ray powder diffraction and elemental analyses. Results have shown that the polyol-derived alkoxide compounds are predominately mono-sodium substituted alkoxide that occur as adducts with sodium hydroxide.
Studies of transesterification reactions catalyzed by polyol-derived sodium alkoxide/hydroxide were conducted to evaluate reaction efficiency and kinetics. The reactions catalyzed by the polyol-derived sodium alkoxide/hydroxide successfully achieved comparable biodiesel yield with sodium methoxide (0.5 wt% of equivalent biodiesel yield under reaction conditions of 6:1 methanol to oil mole ratio at 60°C). Additionally, all polyol-derived alkoxide/hydroxide catalysts investigated in these studies were capable of achieving >95 wt% of biodiesel yield after 1.5 h in a single step transesterification reaction. Initial reaction rates (2 min) differed depending on the polyol used in producing the catalyst. The reaction rates over two minutes are in order of increasing activity: sorbitol < xylitol < sodium methoxide < 1,2-propanediol < 1,3-propanediol < glycerol. This result can be associated with release of these polyols in small quantity (<0.5%) as a result of methanol solvation to liberate the methoxide ion as catalytic agent. Presence of these polyols at the beginning of a reaction may help to stabilize the immiscible oil/methanol phase by formation of emulsifier compounds (such as glycerol esters or glycol esters), which in return facilitate the transesterification reaction. In conclusion, the polyol-derived sodium alkoxide/hydroxide catalysts have demonstrated promising qualities to the industry. These catalysts may serve as an alternative solution to lower the cost of biodiesel plant operation without compromising production efficiency.
Advisors/Committee Members: Reaney, Martin, Sammynaiken, Ramaswami, Dalai, Ajay, Shand, Phyllis.

► Hydrogen has been regarded as the most environmental friendly energy carrier due to its easily-storage and high energy concentration. A variety of technologies have been…
(more)

▼ Hydrogen has been regarded as the most environmental friendly energy carrier due to its easily-storage and high energy concentration. A variety of technologies have been studied to generate hydrogen. Ethanol steam reforming is one of the most promising ways to generate hydrogen since its high productivity. However, the high operating temperature is the main challenge for developing the process. Metallic catalysts have been widely investigated to improve the performance of ethanol steam reforming process. Ni-based catalysts are frequently studied due to their good catalytic performance and low cost for ESR. However, quick deactivation is still a major challenge for Ni-based catalysts, which is mainly caused by coke formation or metal sintering.
In this thesis, improvements of Ni-based catalysts have been studied in two approaches: introducing a second metal of Cu to form bimetallic catalysts and Optimizing Ni content in catalysts that Ni is supported on CaO modified Al2O3. Bimetallic CuNi/YSZ catalysts were synthesized by impregnation. Results showed that adding Cu to Ni-based catalysts successfully improved the catalytic stability while Cu has barely activity in ESR. The formation of Cu-Ni alloy can improve catalyst reducibility and stabilize Ni from sintering. Ni supported on CaO modified Al2O3 catalysts were synthesized by co-precipitation. Introducing of CaO to Al2O3 support successfully improved the stability of catalysts by reducing acidity sites since the acidic property of Al2O3 leads to serious coke formation in ESR. Different Ni loading ratios contribute to the formation of different Ni-containing compounds, which have various catalytic performances in ESR. Increasing Ni loading ratio has positive effect on catalytic activity. But excess Ni loading does influence the particle size, metal dispersion and reducibility.

► This thesis focuses on the understanding the effect of various factors, such as physical structures of metal particles, chemical composition of supports and metal-support interactions,…
(more)

▼ This thesis focuses on the understanding the effect of various factors, such as physical structures of metal particles, chemical composition of supports and metal-support interactions, on the catalytic performance of Pd or Pt nanocatalysts for hydrodeoxygenation (HDO) of bio-oil model compounds.
The first part of the thesis addressed the alternative catalyst synthesis strategy based on emerging double-flame spray pyrolysis method (FSP), which was able to tune the catalytic properties of nanocatalysts without changing their precursors and chemical compositions during the synthesis. A series of Pd catalysts on the silica-alumina supports, SiO2- , and Al2O3 supports have been synthesized with the tunable surface properties within micro-seconds. The characterization results showed that various flow rates of precursors and gases used for the synthesis of catalysts influenced the formation of the catalyst structures and further change the surface acidity of catalysts due to the correlation between acidity and structure, but, the flow rates did not influence the electronic properties of Pd particles. Therefore, the higher conversion but the similar chemoselectivity have been reached in the hydrogenation of the bio-oil model ketone compound-acetophenone
The second part is to identify the dominant effects from size of metal catalysts (under uniform shape and face) or the support acidity in the hydrodeoxygenation of the bio-oil model compounds of acetophenone, benzaldehyde, and butyrophenone. The uniform cubic Pd particles with different size (8, 13, and 21 nm) have been synthesized and loaded on the most popular supports (SiO2-, Al2O3-, and silica-alumina) with various functional groups and acidity. The results showed different acidities on the supports (Brønsted acidic site for Silica-alumina, Lewis acidic site for Al2O3-, and non/weak silanol OH group for SiO2- support) could not influence the chemoselectivity of the reaction but effected the conversion obviously. The particle size has more significant influence than the acidity. The smallest (8nm) Pd particle catalysts regardless of kinds of supports revealed the highest conversion for the hydrogenation the bio-oil model compounds.
The third part focused on the influence of various types of catalysts with different acidities, chemical composition, and metal-support interaction on enantioselective hydrogenation of several model compounds in two reaction systems: 1). Pt-cinchrona modified system, and 2). Pd-(S) proline modified system. The result indicated acidic supports promoted the both conversion and enantioselectivity. Specially, Pd/SA made by double-FSP method, which has the highest Brønsted acid sites, showed 100 % conversion of isopherone on 60 min with 99% ee values.